Problem: $ { {-3} \times \left[\begin{array}{rr}{2} & {3} \\ {-1} & {1} \\ {3} & {1}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-3}\times{2} & {-3}\times{3} \\ {-3}\times{-1} & {-3}\times{1} \\ {-3}\times{3} & {-3}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-6} & {-9} \\ {3} & {-3} \\ {-9} & {-3}\end{array}\right]}$